Half of major forests may be lost by 2100: scientists

HEATING UP Simulations of climate change over the next century show that a small rise in temperatures could kill off 60 percent of forests around the planet

THE GUARDIAN , LONDON

More than half of the world's major forests will be lost if global temperatures rise by an average of 3oC or more by the end of the century, it was claimed on Monday.

The prediction comes from the most comprehensive analysis yet of the potential effects of human-made global warming.

Extreme floods, forest fires and droughts will also become more common over the next 200 years as global temperatures rise owing to climate change, according to Marko Scholze of the University of Bristol.

Scholze took 52 simulations of the world's climate over the next century, based on 16 different climate models, grouping the results according to varying amounts of global warming they predicted by 2100: less than 2oC on average, 2oC to 3oC and more than 3oC. He then used the simulations to work out how the world's plants would be affected over the next few hundred years. The results were published on Monday in the Proceedings of the National Academy of Sciences.

Alan O'Neill, science director for the National Center for Earth Observation, said: "Some work in this area has been done before looking at the meteorological forecasts for climate change and feeding those into vegetation models ... this is a much more comprehensive study."

He added that Scholze's results would give climate scientists the most accurate scientific projection yet of the future effects of global warming.

Scholze said the effects of a 2oC category were inevitable. This is the temperature rise that will happen, on average, even if the world immediately stopped emitting greenhouse gases. This scenario predicts that Europe, Asia, Canada, central America and Amazonia could lose up to 30 percent of its forests.

A rise of 2oC to 3oC will mean less fresh water available in parts of west Africa, central America, southern Europe and the eastern US, raising the probability of drought in these areas.

In contrast, the tropical parts of Africa and South America will be at greater risk of flooding as trees are lost.

Scholze says a global temperature rise of more than 3oC will mean even less fresh water. Loss of forest in Amazonia and Europe, Asia, Canada and central America could reach 60 percent.

A 3oC warming could also present a yet more dangerous scenario where the temperatures induce plants to become net producers of carbon dioxide.

"As temperatures go up, plants like it better and they start to grow more vigorously and start to take up more carbon dioxide from the air," O'Neill said.

"But there comes a point where the take-up is saturated for a given vegetation cover, then the ecosystem starts to respire more than it's taking up," he said.

Scholze's work shows that this so-called "tipping point" could arrive by the middle of this century.